Footwear can be constructed with simple or complex structures. Simple “flip flop” sandals can be formed of a one piece sole cut from foamed rubber or plastic sheet stock with one or two straps attached to hold the sole to the wearer's foot. Other sandals can be formed with a one or two layer sole and again one or more simple straps. Clogs and the like can be formed with a one piece molded or carved sole, in some cases with the carving or molding extended to create an integral “upper” which can serve to affix the sole to the wearer's foot. Molded and carved clogs and like items of footwear are commonly extremely rigid and inflexible.
More complex footwear constructions often involve an outsole which in use contacts the ground, and an insole, which contacts the sole of the wearer's foot and often a midsole located between the outsole and insole to provide shape and structure to the footwear item. One or more straps and/or an upper are affixed to the sole as just described. This more complicated sole construction is more expensive and in certain settings relatively inflexible and not particularly comfortable but offers advantages of providing a defined structure to the article while being relatively adaptable to the wearer's feet.
A variety of United States patents describe footwear articles and the materials and configurations of their construction. These patents include, for example, the following: U.S. Pat. No. 1,053,442, issued Feb. 18, 1913 to Rouse; U.S. Pat. No. 1,964,705 issued Jun. 26, 1934 to Pellhofer; U.S. Pat. No. 2,590,648 issued Mar. 25, 1952 to Pitz; U.S. Pat. No. 4,290,212 issued Sep. 22, 1981 to Matsson; U.S. Pat. No. 4,400,894, issued Aug. 30, 1983 to Ehrlich; U.S. Pat. No. 4,573,457 issued Mar. 4, 1986 to Parks; and U.S. Pat. No. 6,065,230 issued May 23, 2000 to James each of which discloses articles of footwear which have a sole rendered flexible by one or more joints located in the ball of the foot region. Other United States patents of interest include the following: U.S. Pat. No. 2,669,036 issued Feb. 16, 1954 to Isreal; U.S. Pat. No. 5,481,814 issued Jan. 9, 1996 to Spencer and U.S. Pat. No. 3,742,625 issued Jul. 3, 1973 to Famolare each of which shows articles of footwear having a bendable joint in the mid arch region.